[R] metafor package

John Peterson john.peterson.can at gmail.com
Tue Dec 8 14:24:55 CET 2015


Hi Dr. Viechtbauer,

The code provided in the metafor projects website for subgroup includes
fitting a random effects model on the entire dataset and fitting a random
effects model within subgroups. When I exactly follow this code, my
estimates and confidence intervals for estimate within each subgroup
matches with what I get in STATA so it seems to be the correct estimate
(and CI). However, I don't want to present an overall effect and I want to
present only the effect within each subgroup. In my second attempt, I did
not run a random effects model within the entire dataset and only ran the
models within each subgroup. I generated a variable corresponding to the
estimate(risk ratio) and standard error  which I plugged in the forest()
function (i.e. forest(rr, se, .....).  When I run this code, the estimate I
get for each subgroup is slightly different than the estimate I get for
each subgroup in comparison to when I also included the random effects
model for the overall effect. (i.e. my first attempt). Is this the right
approach? I was not clear when you said passing the estimates and sampling
variances to the forest() function. I created a variable corresponding to
the estimate and standard error and plugged those in the forest() function.
I am not sure if this is the right approach. Thanks,

John

On 8 December 2015 at 03:47, Viechtbauer Wolfgang (STAT) <
wolfgang.viechtbauer at maastrichtuniversity.nl> wrote:

> Hi John,
>
> Please keep r-help copied on the reply.
>
> What's the 'previous model'? How do you get estimates within subgroups
> that 'includes the overall effect'? I really cannot follow you here.
>
> Best,
> Wolfgang
>
> --
> Wolfgang Viechtbauer, Ph.D., Statistician | Department of Psychiatry and
> Neuropsychology | Maastricht University | P.O. Box 616 (VIJV1) | 6200 MD
> Maastricht, The Netherlands | +31 (43) 388-4170 | http://www.wvbauer.com
>
> > -----Original Message-----
> > From: John Peterson [mailto:john.peterson.can at gmail.com]
> > Sent: Monday, December 07, 2015 22:14
> > To: Viechtbauer Wolfgang (STAT)
> > Subject: Re: [R] metafor package
> >
> > Hi Dr. Viechtbauer,
> > Thank you very much for your reply. I tried your advice and was able to
> > make a forest plot with only the estimates for each subgroup.For the
> > estiamte for each subgroup, similar to the previous model, I random
> > effects model within each subgroup. However, I now find the result for
> > the estiamte within subgroup to be different thant the result for the
> > previous model. I have tried analyzing this in STATA and I get the same
> > result as the model which includes the overall effect. Any advice on what
> > may be wrong here? Thanks greatly,
> > John
> >
> > On 7 December 2015 at 04:02, Viechtbauer Wolfgang (STAT)
> > <wolfgang.viechtbauer at maastrichtuniversity.nl> wrote:
> > The code you posted is totally mangled up, but it's just what can be
> > found here:
> >
> > http://www.metafor-project.org/doku.php/plots:forest_plot_with_subgroups
> >
> > If you don't want an overall estimate, just pass the estimates and
> > corresponding sampling variances to the forest() function (and not the
> > model object). Use the 'rows' argument to specify where the estimates
> > will be placed and adjust 'ylim' so give you enough space to leave gaps
> > for headings and the subgroup estimates. Then fit models within the
> > subgroups (the 'subset' argument is useful here) and use addpoly() to add
> > the subgroup estimates in the appropriate rows. With text(), you can add
> > headings as needed.
> >
> > If you use weights() on each subgroup model object, you can get the
> > subgroup weights (that add up to 100% within each subgroup). It's
> > probably easiest to just add those values with text() in an appropriate
> > place to the plot.
> >
> > Best,
> > Wolfgang
> >
> > --
> > Wolfgang Viechtbauer, Ph.D., Statistician | Department of Psychiatry and
> > Neuropsychology | Maastricht University | P.O. Box 616 (VIJV1) | 6200 MD
> > Maastricht, The Netherlands | +31 (43) 388-4170 | http://www.wvbauer.com
> >
> > > -----Original Message-----
> > > From: R-help [mailto:r-help-bounces at r-project.org] On Behalf Of John
> > > Peterson
> > > Sent: Monday, December 07, 2015 01:39
> > > To: r-help at r-project.org
> > > Subject: [R] metafor package
> > >
> > > Hi Everyone,
> > >
> > > I am conducting a meta-analysis using the metafor package. I am
> > > interested
> > > in obtaining an estimate by subgroup only without showing an overall
> > > effect. This is directly from the metafor website. How would i modify
> > > this
> > > code to only show subgroup effects? Further, I want to show weights by
> > > subgroup. The option showweights=TRUE does not display weights by
> > > subgroup
> > > but by the weight of each study in comparison to all studies (and not
> > the
> > > subgroup). You help would be appreciated.
>
> [snip garbled code]
>
>

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